Noise generated by a vibratory feeder bowl consists of two main components: noise generated by the parts being fed, and noise generated by the vibratory feeder bowl itself. Part noise is caused by part to part contact and pan: to bowl contact and usually manifests itself as a "rattle". Spectrally, this noise is broad band and usually above 300 Hz. Traditionally, this noise is treated passively by enclosing the vibratory feeder bowl. Such enclosures are frequently treated with sound absorbing foam as well as various damping treatments which are effective at higher frequencies, where part noise dominates.
The second component of vibratory feeder bowl noise is tonal noise caused by the motion of the vibratory feeder bowl. This noise is primarily periodic corresponding to the primarily sinusoidal excitation of the bowl. This periodic or tonal noise manifests itself as acoustic noise and mechanical vibration. Acoustic noise refers to the noise caused by the piston like motion of the vibratory feeder bowl. Acoustic noise is readily identifiable as a low tone or hum. This tone occurs at the primary operating frequency and its harmonics. Typical primary operating frequencies are 50, 60, 100, or 120 Hz. Vibratory feeder bowl users and manufacturers have attempted to attenuate this tonal noise by the use of enclosures. Although enclosures often redistribute the radiation pattern of the tonal noise, they typically do little to attenuate it.
Mechanical vibration is caused by the vibratory feeder bowl imparting vibration to the table on which it is mounted. Vibratory feeder bowls are usually mounted on soft elastomeric pads which reduce the forces transmitted to the mounting surface but do not eliminate them. The force transmitted through a passive mount is related to the ratio of the mass of the mounted device to the stiffness of the mount. Softer mounts allow less force to be transmitted to the mounting surface, thereby reducing the vibration caused by the vibratory feeder bowl. However, sorer mounts allow larger gross motions of the vibratory feeder bowl to occur when it is bumped or when parts are added. Such gross motions can cause the output track of the vibratory feeder bowl to exceed alignment tolerances causing parts jams and interrupting production. So in considering the stiffness of a mount, alignment tolerances are traded off against vibration transmitted by the mount.
Mechanical vibration can cause acoustic radiation. Because of the relatively large surface area of the table on which vibratory feeder bowls are usually mounted, small vibrations can cause effective acoustic radiation. Furthermore, vibration of the table induces vibration in the floor, which can also radiate acoustic energy. Table vibration often reduces the capability of the vibratory feeder equipment to feed parts. A reduction in vibration is desirable from a mechanical as well as acoustic standpoint.